1. Field of the Invention
The present invention relates to fluid fill and relief valves. More specifically, the invention relates to an assembly combined fill and relief valve contained within a singular housing.
2. Description of Related Art
Fill valves are commonly configured as simple check valves which permit fluid flow in one direction (e.g., from inlet to outlet) but not in the reverse. Such valves are provided with inlet and outlet ports and function generally to permit fluid flow therethrough from inlet to outlet when the pressure at the inlet exceeds that at the outlet (an additional amount of pressure may be needed to overcome a small spring force used to bias the valve closed), and to prevent fluid flow therethrough from outlet to inlet when the pressure at the outlet exceeds that at the inlet. Use of a check-type fill valve alone may be inadequate because the pressure of the fluid introduced to a fluid chamber to which the valve is coupled may exceed the limitations of the fluid chamber. For this reason check-type fill valves are often used in conjunction with a separate relief valve.
Relief valves are designed to prevent backflow from the outlet until pressure on a valve element overcomes a force biasing the valve element against a valve seat, after which the valve opens, releasing pressure so that pressure of fluid in the fluid chamber may be maintained at or below a desired maximum pressure. Therefore, the use of a relief valve in conjunction with a fill valve allows pressure to build within the fluid chamber to a desired level while preventing damage to the fluid chamber to which the valve is attached by allowing excess fluid to be vented.
Some configurations of a fluid chamber and some environments present space limitations which prevent the use of separate fill and relief valves. Where there is only room for one valve, a fill valve may be used to prevent backflow of fluid from outlet to inlet. However, use of a fill valve alone will allow a buildup of fluid pressure within the fluid chamber until some component of the valve or fluid chamber fails. The fluid chamber may be designed to fail at a pre-set maximum pressure, but replacement of a failed fluid chamber represents an expensive and time-consuming process which might be eliminated with the inclusion of a relief valve.
The combination of fill and relief valves in a single housing is known. For example, U.S. Pat. No. 1,004,986, the disclosure of which is hereby incorporated by reference, shows a safety valve for pneumatic tires which is designed to prevent explosion of a tire due to excessive air pressure. Two valves are provided in a single casing. The mechanism includes a valve stem which is slidable so that, upon actuation of the relief valve, a portion of the valve stem is slid to the exterior of the casing and exposed to the surrounding atmosphere. The valve stem returns when the excess pressure is abated. Such a valve is not viable in a dirty environment because contaminants such as dirt particles are likely to be introduced which may affect the proper function of the valves. Also, the axial movement of the valve stem outside the housing is undesirable because the stem may more easily be broken off.
U.S. Pat. No. 3,747,626, the disclosure of which is hereby incorporated by reference, teaches a combined fill and relief valve. The fill valve is spring-biased toward an open position as shown in FIG. 1, so that dirt or other contaminants may more easily be introduced. Also, the valve elements are of complex shape including "nipple-like protrusions" and complementary depressions.
These and other conventional valves which combine relief and fill check functions are not suitable for applications in dirty environments. A further shortcoming of conventional valves is their failure to provide features to prevent sudden loss of pressure as the valve is removed Therefore the use of such a valve with grease, for example, presents a possibility of an undesirable sudden expulsion of grease or the valve housing itself (possibly toward the operator) when the valve is unseated from the fluid chamber.